To retrieve data from Slack, you need to interact with the Slack API. Start by creating a Slack app through the Slack API site. Once your app is created, note the OAuth token provided. This token will be used to authenticate requests to the Slack API and access the desired data.

Determine the specific data you need from Slack, such as messages from a specific channel or user information. This will guide which Slack API methods you'll need to call. For messages, you might use the `conversations.history` API method, while for user data, you might use `users.list`.

Develop a script using a programming language like Python to fetch data from Slack. Use the `requests` library to make HTTP requests to the Slack API endpoints. For example:
```python
import requests

slack_token = 'your-slack-oauth-token'
headers = {'Authorization': f'Bearer {slack_token}'}
response = requests.get('https://slack.com/api/conversations.history', headers=headers, params={'channel': 'channel_id'})
slack_data = response.json()
```
Ensure error handling is in place to manage any issues during the API requests.

Once you have the data from Slack, transform it into a format suitable for insertion into a MySQL database. This may involve data cleaning or restructuring, such as converting timestamps to a MySQL-compatible format or flattening nested JSON structures.

Ensure your MySQL server is running and accessible. Create a database and the necessary table(s) to store the Slack data. Use SQL commands to define the schema based on the data structure you have extracted from Slack. For instance:
```sql
CREATE DATABASE slack_data;
USE slack_data;
CREATE TABLE messages (
id INT AUTO_INCREMENT PRIMARY KEY,
user VARCHAR(100),
text TEXT,
timestamp DATETIME
);
```

Use a database connector in your script, such as `mysql-connector-python`, to insert the transformed data into the MySQL table. For example:
```python
import mysql.connector

connection = mysql.connector.connect(
host='localhost',
user='your_username',
password='your_password',
database='slack_data'
)
cursor = connection.cursor()

for message in slack_data['messages']:
cursor.execute(
"INSERT INTO messages (user, text, timestamp) VALUES (%s, %s, %s)",
(message['user'], message['text'], message['ts'])
)
connection.commit()
connection.close()
```

To keep the data updated, automate the data transfer process. You can use a task scheduler like cron (on Unix-based systems) or Task Scheduler (on Windows) to run your script periodically. Ensure your script logs its operations and any errors for troubleshooting.

By following these steps, you can effectively move data from Slack to a MySQL database without relying on third-party connectors or integrations.